Bendable metal duct

ABSTRACT

The disclosed bendable metal duct is capable of being formed into sharp bends without rupture of the duct seams. Metal strip, which has been corrugated substantially in the direction of its longitudinal axis to provide flexibility in the finished duct, is helically wound into tubular shape. The duct convolutions are joined by a lock seam which is secured by crimps disposed along the length of the seam at an acute angle to the longitudinal axis thereof. Each crimp carries through the layers of the seam to form a series of detents engaging between said layers to prevent slippage and seam rupture upon the application of bending stresses to the duct. The apparatus for automatically and continuously forming the bendable metal duct includes rollers for corrugating the strip, and a forming head on which the strip is helically wound. It also includes means for forming the lock seam comprising a crimping wheel having gearlike teeth for crimping the seam, and a press wheel to insure that the crimped seam lies flat and that the detents thereof properly engage.

United States Patent [72] inventors Richard B. Pelley East Kingston, N.1-1.; Norman Peltier, Amesbury, Mass. [21] Appl. No. 773,061 [22] Filed Nov. 4, 1968 [4S] Patented Sept. 14, 1971 [73] Assignee Callahan Mining Corporation New York, N.Y.

[54] BENDABLE METAL DUCT 4 Claims, 18 Drawing Figs.

[51] Int. Cl F161 9/16, B2lc 37/12, B2lf35/02 [50] Field of Search 72/49, 50,

Primary Examiner-Charles W. Lanham Assistant Examiner-R. M. Rogers Att0rneyJohn C. Blair ABSTRACT: The disclosed bendable metal duct is capable of being formed into sharp bends without rupture of the duct seams. Metal strip, which has been corrugated substantially in the direction of its longitudinal axis to provide flexibility in the finished duct, is helically wound into tubular shape. The duct convolutions are joined by a lock seam which is secured by crimps disposed along the length of the seam at an acute angle to the longitudinal axis thereof. Each crimp carries through the layers of the seam to form a series of detents engaging between said layers to prevent slippage and seam rupture upon the application of bending stresses to the duct. The apparatus for automatically and continuously forming the bendable metal duct includes rollers for corrugating the strip, and a forming head on which the strip is helically wound. 1t also includes means for forming the lock seam comprising a crimping wheel having gearlike teeth for crimping the seam, and a press wheel to insure that the crimped seam lies flat and that the detents thereof properly engage.

PATENTEDSEPMIBYI 36041464 SHEET 4 OF 4 'BENDABLE METAL DUCT BACKGROUND'OF THE INVENTION Industrial air control which includes air conditioning and air and fume handling requires the .use of substantial quantities of ductwork. In the past the familiar sheet metal duct usually of squarish cross section hasbeen extensively used for this-purpose. Problems arise, however, in the use of such duct. It is rigid and accordingly must be manufactured to approximate size for particular installations. Thereafter a great deal of cutting and fitting is required on the job to achieve the desired fit needed. In those areas where sheet metal duct must be shaped to avoid obstructions or fit around comers, substantial cutting and piecing with brazing or soldering is required, and often transition ductwork shapes are necessary to make a bend or the like.

Some of these problems have been overcome with the use of flexible, reinforced fabric hose. Such hose can be readily bent around obstructions or corners without cutting or seaming, and it can be stretched or compressed in situ to provide the precise length needed.

For certain applications, however, the physical properties of metal duct are required. For example, where internal duct pressures must be maintained substantially above or below ambient pressure, the wall strength of the duct must be sufficient to prevent bursting or collapse. Also, metal duct is desirable where there may be exposure to conditions of high or low temperature abrasion or corrosive attack.

To meet these requirements, flexible metal duct has been developed which combines many of the desirable features of both sheet metal duct and flexible hose. The prior art flexible metal duct, however, has been severely limited in the amount of flexure or bending it will withstand. In particular, the seams of prior art flexible metal duct have been weak and subject to rupture at bending stress levels below those required for approval by major testing laboratories.

Accordingly, representative objects of the present invention are to provide bendable metal duct capable of meeting or exceeding the bending stress requirements of standards testing laboratories, and which is attractive, economical, easily installed and lends itself to automated production; and to provide a method and apparatus for the manufacture of such duct.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, the apparatus embodying features of construction, combinations and arrangement of parts which are adapted to effect such steps, and the article which possesses the characteristics, properties and relation of elements, all as exemplified in the detailed disclosure hereinafter set forth and the scope of the invention will be indicated in the claims.

SUMMARY OF THE INVENTION The duct of the invention is a strong, lightweight and hand bendable conduit for use in all types of industrial air control. Its bendable nature permits the installer to fit the duct around obstructions or around corners without the cutting, piecing and attendant labor required with prior art rectangular metal duct.

The duct is formed with a novel lock seaming technique along the interlocking edges of the spiral strip forming such duct. This produces crimped seams that are highly resistant to rupture under bending stress. Accordingly, the duct of the invention can be formed into sharp bends and tortuous shapes not possible with prior art materials.

An automated apparatus is provided to produce the bendable duct of the invention in commercial quantities. Metal strip, for example of aluminum, electrogalvanized steel or stainless steel, is continuously fed from a supply roll through a series of corrugating rolls; these produce corrugations in the strip which give the finished duct its flexibility. Forming rolls then prepare the edges'of the strip for seaming. From the forming rolls the strip is helically wound into tubular form and the edges of adjacentconvolutions of the helically wound strip are interlocked to produce a lock seam which winds helically around the duct.

The lock seam is secured by crimping it with a rotating crimping wheel. The crimping wheel has teeth protruding from the periphery thereof in the manner of a gear which press into and deform or crimp the metal layers of the seam to produce a series of detents which interengage between the metal layers. The detents are preferably disposed to form an acute angle with the longitudinal axis of the seam so that lateral movement between layers 'of the seam is greatly inhibited when the finished duct is bent.

The seam formed in accordance with the invention has been found to be highly resistant to rupture under bending stress. Accordingly, the resultant duct is capable of meeting and exceeding the exacting requirements of standards testing laboratories for approval in air conditioning and other air control applications.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a somewhat schematic side elevation view of an apparatus for forming bendable metal duct, in accordance with the invention.

FIG. 2 is a top plan view of the apparatus of FIG. 1 illustrating the formation of a length of bendable, metal duct.

FIGS. 3-9 are enlarged, partial sectional views taken along lines 3-3 through 9-9 of FIG. 1 and illustrating stages in the formation of the duct of the invention.

FIG. 10 is an enlarged perspective view of the forming head of the apparatus of FIG. 1.

FIG. 11 is a perspective view of the spiral assembly of the forming head.

FIG. 12 is a greatly enlarged, partial sectional view taken along line 12-12 of FIG. 1 and illustrating the formation of the duct seam.

FIG. 13 is a greatly enlarged, partial sectional view taken along line 13-!3 of FIG. 1 and illustrating the operation of the crimping wheel of the invention.

FIG. 14 is a partial sectional view taken along line 14-14 of FIG. 13.

FIG. 15 is a partial sectional view taken along line 15-15 of FIG. 13.

FIG. 16 illustrates another embodiment of the crimping wheel of the invention.

FIG. 17 is a greatly enlarged, partial sectional view taken along line 17-17 of FIG. 1.

FIG. 18 is a greatly enlarged, top plan view of the crimped seam on the bendable duct of the invention taken along line 18-18 ofFIG. 17.

Similar reference characters refer to similar parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specifically, referring to FIG. 1, there is shown apparatus for forming bendable metal duct in accordance with the invention. Metal strip 20, typically aluminum, electrogalvanized steel or stainless steel preferably having a thickness of about 0.005 to 0.008 inches, is first fed from a supply (not shown) through a lubricating tank 22. A series of rollers 24, 26 and 28 around which strip 20 is threaded in tank 22 cause the strip to be immersed in a lubricant 30. Lubricant 30 is preferably a soap base variety which serves the dual function of cleaning the strip and providing a lubricating film on the surface thereof to facilitate subsequent metal working operations.

Metal strip of the type used in the invention often will twist and bend as it unrolls from the supply. Accordingly, strip 20 is passed from tank 22 under a pair of flattening rolls 32 and 34 which press the strip against an anvil 36 to straighten out bends and twists; this helps to prevent the strip from binding or jamming in the metal forming portions of the apparatus.

Still referring to FIG. 1, strip 20 is then passed through a series of corrugating roller pairs 38a-38b, ma-40b, 42a-42b, 44a-44b, and 46a-46b which corrugate the strip to provide flexibility in the finished duct; each roller pair as shown in FIGS. 3-7 comprises mating interfitting corrugating portions consisting of ridges and grooves formed in the roll periphery. As strip 20 passes between the roller pairs 38 through 46 the rollers act to sequentially deform the metal strip 20, thus forming a plurality of corrugations 47 (FIG. 7) substantially parallel to the strips longitudinal axis. While nine corrugations have been shown in strip 20 in FIG. 7, the number may vary depending upon strip width and the degree of flexibility desired in the finished duct. Preferably, as shown in FIGS. 3-7, the metal deformation which produces corrugations 47 is effected alternately about the centerline of strip 20 by the roller pairs. It is found that the sequential and alternating method of metal deformation used contributes to smoothness and uniformity of the corrugations.

From the corrugating rollers 38 through 46, strip 20 passes sequentially between pairs of forming rollers 48a-48b and 5011-50 (FIGS. 8 and 9). Roller pairs 48 and 50 have interfitting grooves and ridges which receive the corrugations 47 previously formed so as to maintain the strip in axial alignment. In addition, rollers 48a and 48b have mating chamfered corners 52a and 52b (FIG. 8) at either end thereof which serve to partially bend the edges 54 and 56 of strip 20 in opposite directions in preparation for lock seaming. The bending of the strip edges 54 and 56 begun by rollers 48a and 48b is completed by rollers 50a and 50b as shown in FIG. 9. Strip edges 54 and 56 are bent at right angles in the space between the adjacent shoulders 58a and 5812 at either end of roller pair 50a-50.

Strip 20 with its edges 54 and 56 bent as described is then fed to the forming head 62 of the apparatus (FIG. 1) for formation into bendable duct 63 as shown in FIG. 2. Forming head 62 comprises a spiral assembly 64 (FIG. 11) fixedly secured by bolts 66 to the apparatus frame and supported on a fixed mandrel 68 as shown in FIG. 10. Mandrei 68 has a diameter equal to the desired duct diameter and is secured to the apparatus frame by a bolt 70 which makes it interchangeable with other similar mandrels having diameters of other duct slzes.

Spiral assembly 64 comprises a tubular member 72 (FIG. 11) mounted at one end to support plate 74 and having the other end machined to produce a spiral surface 76. Surface 76 is given a pitch P (FIG. 11) equal to the pitch P (FIG. 2) desired in the helical windings of the bendable duct; a number of interchangeable spiral assemblies with appropriately pitched spiral surfaces may be provided for various size duct. A plurality of guide fingers 78 extend from the leading edge 79 of spiral assembly 64. Fingers 78 are curved to match the curvature of tubular member 72 and are pitched at an angle from leading edge 79 to match the pitch of spiral surface 76. Fingers 78 conform in number and spacing to the corrugations in strip 20.

As shown in FIGS. 2 and 12, as strip 20 is fed around mandrel 68, the inner edge 54 thereof contacts spiral surface 76 which forces the strip to spiral about mandrel 68 at the predetermined pitch. Also the corrugations on the strip engage fingers 78 (FIG. 12) which serve to guide the strip and prevent it from slipping out of the desired spiral path.

The successive convolutions of the duct which is formed are secured by a lock seam. Referring to FIG. 2, adjacent convolutions 20a and 20b of the strip 20 supported on forming head 62 first pass under a pointer 80. As shown in FIG. 10, pointer 80 is mounted over mandrel 68 in a sleeve 81 secured to a bracket 82; it is slidable within sleeve 81 so that its position relative to mandrel 68 may be adjusted for different sizes of duct, and it is secured in a desired position in sleeve 81 by means of a set screw 83. As discussed above, one edge 54 of strip 20 is bent up while the opposite edge 56 is bent down so that adjacent successive convolutions on forming head 62 have adjacent edges which are oppositely directed. As shown in FIG. 12, the tip of pointer is positioned (by the angle of bracket 82 and by adjustment through screw 83) to force the downward directed edge 56 on one convolution to overlap and be tucked under the adjacent upwardly directed edge 54 of the preceding convolution. This is the first step in the formation of the lock seam.

The overlapped edges 54 and 56 next pass under a seaming wheel 84 supported on a shaft 85 in an adjustable holder 86 as shown in FIG. 10. Holder 86 is mounted on an adjustment screw 87 which permits wheel 84 to be adjusted vertically with respect to mandrel 68. Adjustment screw 87 and shaft 85 are in turn mounted to the apparatus frame on a holder (not shown) which permits the entire assembly to be moved parallel to the axis of mandrel 68 for accurate positioning of wheel 84. The orientation of wheel 84 relative to mandrel 68 may also be adjusted by twisting shaft 85 in the holder 86. As shown in FIGS. 10 and 12, seaming wheel 84 is tilted on shaft 85 at an angle to mandrel 68. The unsupported front end 88 of wheel 84 is beveled (FIG. 12) and an enlarged ridge 89 is provided at a distance from unsupported end 88 approximately equal to the width of the lock seam being formed. As the overlapped edges 54 and 56 pass under wheel 84 they are wedged together by pressure from ridge 89 and are bent down to a partially flat position by beveled end 88 to form a lock seam 91 (FIGS. 2).

The lock seam 91 joining successive convolutions of the duct next passes under a crimping wheel (FIG. 2) rotatably supported on a shaft 93 mounted in a yoke adjacent mandrel 68 as shown in FIG. 10. Referring to FIGS. 13 and 14, crimping wheel 90 is formed with a band of raised crimping teeth 92 extending across the periphery thereof in the manner of gear teeth. Crimping teeth 92 are preferably similar to the teeth of a helical gear, that is, they are formed at an angle to the axis of wheel 90 as shown in FIG. 13. With crimping teeth of the helical type, crimping wheel 90 may be positioned adjacent forming head 62 with its axis parallel to the mandrel axis as shown in FIG. 2; it will be understood, however, that crimping wheel 90 may also have crimping teeth which are parallel to the wheel axis in the manner of a spur gear. Such a crimping wheel may be used in the apparatus of the invention by mounting it with its axis tilted to the axis of mandrel 68 to produce the desired diagonal crimps.

As the lock seam joining successive convolutions of strip 20 advanced from seaming wheel 84 it passes, under pressure, between crimping teeth 92 and mandrel 68. It will be noted from FIGS. 2 and 10 that crimping wheel 90 is positively driven by a gear 94 journaled to crimping wheel shaft 93; gear 94 is in turn driven by a main driving gear 98 connected to a motor or other source of power. Thus, the convolutions of duct 63 are positively driven around mandrel 68 by frictional and mechanical engagement with crimping teeth 92. As the convolutions rotate under crimping wheel 90, crimping teeth 92 are pressed into the surface of the lock seam, as shown in FIGS. 13 and 14, and deform the metal layers thereof to produce a continuous string of depressions or crimps 100 over the length of the seam. The pressure exerted between crimping wheel 90 and the lock seam 91 is adjusted so that each crimp 100 projects through the successive metal layers of the seam to form a series of detents 102 which engage between the seam layers as shown in FIGS. 14 and 17.

Because the crimping wheel teeth 92 are preferably positioned diagonally on the crimping wheel periphery, crimps 100 are formed at an acute angle a with the longitudinal axis of the lock seam as shown in FIG. 18. The crimps may slope upwardly from left to right as shown in FIG. 18 or may be rotated 90 with substantially similar results. Also the acute angle at which the crimps are formed may vary over wide limits; preferably however the angle will be maintained between about 30 and about 60, and for optimum seam strength will be about 45. The unique engagement of the angled detents 102 between layers of the lock seam serves to effectively prevent slippage between seam layers upon the application of bending stresses, they thus enable the duct to be bent without danger of seam rupture.

It has been found that duct formed with seams in accordance with the invention can be safely bent around a radius approximately equal to the diameter of the duct, and is capable of withstanding numerous cycles of bending and straightening without damage. This is in distinct contrast to prior art flexible duct in which seam rupture frequently occurs when bends having a radius approaching the duct diameter are attempted.

Preferably, crimping teeth 92 are formed with a slight concavity over the length of their top land surface 104 as shown in FIG. 15. It has been found that the provision of such a concavity results in a more uniform width of crimp on the lock seam and thus more uniform and predictable properties in the duct. It is believed that improved results are obtained because the concavity in the tooth surface serves to more evenly distribute the crimping force over the width of the lock seam.

While the crimped lock seam and the method and apparatus for forming it as described above find particular utility in the bendable metal duct of the invention, it will be appreciated that the crimping technique disclosed herein may be applied to many other types of seamed metal duct subject to bending stresses.

Another type of crimping wheel useful in the invention is shown in FIG. 16. It is similar in all respects to the crimping wheel described in conjunction with FIGS. 13 and 14 except that it contains a second band of crimping teeth 92a; these are disposed on the periphery adjacent the first band 92 but at an angle thereto. The two bands of crimping teeth 92 and 92a thus produce a chevron tooth configuration. A crimping wheel of the type shown in FIG. 16 may be used especially in the formation of large duct sizes where the width of the lock seam may be substantial.

Referring back to FIGS. 1 and 2, after passing under crimping wheel 90, the now crimped lock seam 106 is advanced on mandrel 68 under a press wheel 108. Press wheel 108 is supported adjacent mandrel 68 on a shaft 110 in a yoke 111 FIG. Shaft 110 is journaled to gear 112 which in turn is positively driven by main driving gear 98. The diameters of gear 112 and press wheel 108 are preferably equal to the respective diameters of gear 94 and crimping wheel 90 so that their rates of rotation are equal. In this way press wheel 108 and crimping wheel 90 cooperate to move duct 63 at a uniform rate around mandrel 68 and off the end thereof as a finished product. Press wheel 108 and crimping wheel 90 may, of course, be of different diameters so long as the diameters of their respective gears 112 and 94 are correlated to provide equal peripheral speeds.

The functions of press wheel 108 are to insure that the crimped seam 106 has been sufiiciently flattened so that it does not protrude from the surface of the finished duct, and that detents 102 are all fully engaged between the layers of the lock seam. Accordingly, as shown in FIG. 17, press wheel 108 has a recessed center portion 114 which serves to press flat any portion of crimped seam 106 which protrudes beyond acceptable limits as the seam passes thereunder.

After passing under press wheel 108 duct 63 is completed and as shown in FIG. 2, it feeds off the forming head 62 and may be cut manually or automatically into any desired length. With the apparatus disclosed, bendable duct can be automatically and continuously produced at a high production rate and the duct so produced exhibits the ability to be bent sharply and repeatedly without danger of scam rupture.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in carrying out the above rocess, in the described product, and in the construction set orth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a metal duct having a sidewall comprising helically wound metal strip and a lock seam comprising layers of said strip joining successive convolutions thereof, said lock seam having a plurality of crimps spaced along its length at an acute angle of from about 30 to about 60 to the longitudinal axis of the seam, each said crimp being a deformed portion in substantially all said metal layers of said seam and interengaging between said layers thereby acting to prevent the rupture of said seam upon the application of bending stresses to said duct.

2. A bendable metal duct as defined in claim 1 wherein said sidewall is formed of longitudinally corrugated metal strip.

3. A metal duct as defined in claim 1 wherein said angle is about 45.

4. In a metal duct having a sidewall comprising helically wound metal strip and a lock seam comprising layers of said strip joining successive convolutions thereof, said lock seam having a plurality of crimps spaced along its length which are chevron shaped with acute angles to the longitudinal axis of the seam, each said crimp being a deformed portion in substantially all said metal layers of said seam and interengaging between said layers thereby acting to prevent the rupture of said seam upon the application of bending stresses to said duct. 

1. In a metal duct having a sidewall comprising helically wound metal strip and a lock seam comprising layers of said strip joining successive convolutions thereof, said lock seam having a plurality of crimps spaced along its length at an acute angle of from about 30* to about 60* to the longitudinal axis of the seam, each said crimp being a deformed portion in substantially all said metal layers of said seam and interengaging between said layers thereby acting to prevent the rupture of said seam upon the application of bending stresses to said duct.
 2. A bendable metal duct as defined in claim 1 wherein said sidewall is formed of longitudinally corrugated metal strip.
 3. A metal duct as defined in claim 1 wherein said angle is about 45*.
 4. In a metal duct having a sidewall comprising helically wound metal strip and a lock seam comprising layers of said strip joining successive convolutions thereof, said lock seam having a plurality of crimps spaced along its length which are chevron shaped with acute angles to the longitudinal axis of the seam, each said crimp being a Deformed portion in substantially all said metal layers of said seam and interengaging between said layers thereby acting to prevent the rupture of said seam upon the application of bending stresses to said duct. 